The present invention relates to a replaceable license plate frame structure including a front frame and a rear frame in which the front frame is inserted plush into the rear frame to form a decorative picture. The rear face of the rear frame is formed with a peripheral dent for receiving the license plate. The front and rear frames are engaged to be burglar proof with each other by tenons and mortises and lugs and screws. Multiple front frames with different decorative front faces can be replaceably assembled with the rear frame so as to freely vary the pattern of the entire license plate frame structure.